螺杆压缩机的设计外文文献翻译、中英文翻译、外文翻译

英文原文

Screw Machine Design

Holmes, 1999 reported that even higher accuracy was achieved on the new Holroyd vitrifying thread-grinding machine, thus keeping the manufacturing tolerances within 3 μm even in large batch production. This means that, as far as rotor production alone is concerned, clearances between the rotors can be as small as 12 μm.

Screw machines are used today for different applications both as compressors and expanders.

Fig. 1.4. Screw compressor mechanical parts

Fig. 1.5. Cross section of a screw compressor with gear box

For optimum performance from them a specific design and operating mode is needed for each application. Hence, it is not possible to produce efficient machines by the specification of a

universal rotor configuration or set of working parameters, even for a restricted class of machines. Industrial compressors are required to compress air, refrigerants and process gases. For each application their design must differ to obtain the most desirable result. Typically, refrigeration and process gas compressors, which operate for long periods, must have a high efficiency. In the case of air compressors, especially for mobile applications, efficiency may be less important than size and cost.

Oil free compressed air is delivered almost exclusively by screw compressors. The situation is becoming similar for the case of process gas compression. In the field of refrigeration, reciprocating and vane compressors are continuously being replaced by screw and a dramatic increase in the needs for refrigeration compressors is expected in the next few years.

The range of screw compressors sizes currently manufactured is covered by male rotor diameters of 75 to 620mm and this permits the delivery of compressed gas flow rates of 0.6m3/min to 600m3/min. A pressure ratio of 3.5 is attainable in them from a single stage for dry compressors and up to 15 for oil flooded ones. Normal pressure differences are up to 15 bars, but maximum pressure differences sometimes exceed 40 bars. Typically, for oil flooded air compression applications, the volumetric efficiency of these machines now exceeds 90% and the specific power input has been reduced to values which were regarded as unattainable only a few years ago.

1.1 Screw Compressor Practice

The Swedish company SRM was a pioneer and they are still leaders in the field of screw compressor practice. Other companies, like Compair U.K., Atlas- Copco in Belgium, Ingersol-Rand and Gardner Denver in the USA and GHH in Germany follow them closely. York, Trane and Carrier lead in screw compressor applications for refrigeration and air conditioning. Japanese screw compressor manufacturers, like Hitachi, Mycom and Kobe-Steel are also well known. Many relatively new screw compressor companies have been founded in the Middle and Far East. New markets in China and India and in other developing countries open new screw compressor factories. Although not directly involved in compressor production the British company, Holroyd, are the largest screw rotor manufacturer, they are world leaders in tool design and tool machine production for screw compressor rotors.

Despite the increasing popularity of screw compressors, public knowledge and understanding of them is still limited. Three screw compressor textbooks were published in Russian in the early nineteen sixties. Sakun, 1960 gives a full description of circular, elliptic and cycloidal profile generation and a reproducible presentation of a Russian asymmetric profile named SKBK. The profile generation in his book was based on an envelope approach. Andreev, 1961 repeats the theory of screw profiles and makes a contribution to rotor tool profile generation theory. Golovintsov’s textbook, 1964, is more general but its section on screw compressors is both interesting and informative. Asomov, 1977, also in Russian, gave a reproducible presentation of

the SRM asymmetric profile, five years after it was patented, together with the classic Lysholm Profile.

Two textbooks have been published in German. Rinder, 1979, presented a profile generation method based on gear theory to reconstruct the SRM asymmetric profile, seven years after it was patented. Konka, 1988, published some engineering aspects of screw compressors. Only recently a number of textbooks have been published in English, which deal with screw compressors. O’Neill, 1993, on industrial compressors and Arbon, 1994, on rotary twin shaft compressors. There are a few compressor manufacturers’ handbooks on screw compressors and a number of brochures giving useful information on them, but these are either classified or not in the public domain. Some of them, like the SRM Data Book, although available only to SRM licensees, are cited in literature on screw compressors.

There is an extraordinarily large number of patents on screw compressors. Literally thousands have appeared in the past thirty years, of which SRM, alone, holds 750. The patents deal with various aspects of these machines, but especially with their rotor profiles. The SRM patents of Nilson, 1952, for the symmetric profile, Shibbie, 1979, for the asymmetric profile and Astberg 1982, for the “D” profile are the most widely quoted in reference literature on this topic. Ohman, 1999, introduced the “G” profile for SRM. Other examples of successful profiling patents may also be mentioned, namely: Atlas-Copco,Compair with Hough, 1984, Gardner Denver with Edstroem, 1974, Hitachi with Kasuya, 1983, and Ingersoll-Rand with Bowman, 1983. More recently, several highly successful patents were granted to relatively small companies such as Fu Sheng, Lee, 1988, and Hanbel, Chia-Hsing, 1995. A new approach to profile generation, using a rack as the basis for the primary curves, was proposed by Rinder, 1987, and Stosic, 1996. All patented profiles were generated by a procedure but information on the methods used is hardly disclosed either in the patents or in accompanying publications. Thus it took many years before these procedures became known. Examples of this are: Margolis, who published his derivation of the symmetric circular profile in 1977, 32 years after it had been patented and Rinder, who used gear meshing criteria to reproduce the SRM asymmetric profile in 1979, 9 years after patent publication. It may also be mentioned that Tang, 1995, derived the SRM “D” profile analytically as part of a PhD thesis 13 years after the patent publication. Many other aspects of screw compressors were also patented. These include nearly all their most well known characteristics, such as, oil flooding, the suction and discharge ports following the rotor tip helices, axial force compensation, unloading, the slide valve and the economiser port, most of which were filed by SRM. However, other companies were also keen to file patents. The general impression gained is that patent experts are as important for screw compressor development as engineers There is a surprising lack of screw compressor publications in the technical literature. Lysholm’s papers in 1942 and 1966 were a mid twentieth century exception, but he did not include any details of the profiling details which he introduced to reduce the blow-hole area. Thus,

journal papers like those of Stosic et al., 1997, 1998, may be regarded as an exception. In recent years, publication of screw compressor materials in journals has become more common through the International Institution of Refrigeration Stosic, 1992 and Fujiwara, 1995, the IMechE, with papers by Smith, 1996, Fleming, 1994, 1998 and Stosic 1998, and the ASME, by Hanjalic, 1997. Together these made more information available than the total published in all previous years. Stosic’s, 1998 paper is a typical example of the modern practice of timely publishing.

There are three compressor conferences which deal exclusively or partly with screw compressors. These are the biennial compressor technology conference, held at Purdue University in the USA, the IMechE international conference on compressors and their systems, in England and the “VDI Schraubenkompressoren Tagung” in Dortmund, Germany. Despite the number of papers on screw compressors published at these events, only a few of them contain useful information on rotor profiling and compressor design. Typical Purdue papers cited as publications from which a reader can gain information on this are: Edstroem, 1992, Stosic, 1994 and Singh, 1984, 1990. Zhang, 1992,indicates that they used envelope theory to calculate some geometric features of their rotors. The Dortmund proceedings give some interesting papers such as that by Rinder, 1984, who presented the rack generation of a screw rotor profile, including a fully reproducible pattern based on gear theory. Hanjalic, 1994 and Holmes, 1994, give more details on profiling, manufacturing and control. Kauder, 1994, 1998 and Stosic, 1998 are typical examples of successful university reseach applied to real engineering. Sauls, 1994, 1998, may be regarded as an example of fine engineering work. The London compressor conference included some interesting papers like those of Edstroem, 1989 and Stosic et al., 1999.

Many reference textbooks on gears give useful background for screw rotor profiling. However all of them are limited to the classical gear conjugate action condition. Litvin, 1968 and 1956–1994 may be regarded as an exception to this practice, in giving gearing theory which can be applied directly to screw compressor profiling. 1.2 Recent Developments

The efficient operation of screw compressors is mainly dependent on proper rotor design. An additional and important requirement for the successful design of all types of compressor is an ability to predict accurately the effects on performance of the change in any design parameter such as clearance, rotor profile shape, oil or fluid injection position and rate, rotor diameter and proportions and speed.

Now, when clearances are tight and internal leakage rates have become small, further improvements are only possible by the introduction of more refined design principles. The main requirement is to improve the rotor profiles so that the internal flow area through the compressor is maximised while the leakage path is minimised and internal friction, due to relative motion between the contacting rotor surfaces, is made as small as possible.

Although it may seem that rotor profiling is now in a fully developed state, this is far from